Juergen Burkhardt

Juergen Burkhardt
University of Bonn | Uni Bonn · Institute of Crop Science and Resource Conservation (INRES)

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85
Publications
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3,355
Citations
Citations since 2017
14 Research Items
1510 Citations
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2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300

Publications

Publications (85)
Article
Full-text available
Aerosols can contribute to plant nutrition via foliar uptake. The conditions for this are best at night because the humidity is high and hygroscopic, saline deposits can deliquesce as a result. Still, stomata tend to be closed at night to avoid unproductive water loss. However, if needed, nutrients are on the leaf surface, and plants could benefit...
Article
Full-text available
Major parts of anthropogenic and natural aerosols are hygroscopic and deliquesce at high humidity, particularly when depositing to leaf surfaces close to transpiring stomata. Deliquescence and subsequent salt creep may establish thin, extraordinary pathways into the stomata, which foster stomatal uptake of nutrients and water but may also cause sto...
Article
Full-text available
The recent suggestion of phosphine in Venus’s atmosphere has regenerated interest in the idea of life in clouds. However, such analyses usually neglect the role of water activity, which is a measure of the relative availability of water, in habitability. Here we compute the water activity within the clouds of Venus and other Solar System planets fr...
Article
Full-text available
Maximize process of pest control reducing loss in the agriculture process is fundamental. The aim this research was to achieve a different way to increase the herbicide activity, using potassium salts. Some experiments were conduct to analyze the efficiency of salts in enhanced the activity of two selected herbicides (paraquat and bromoxynil). Firs...
Article
Full-text available
Stomatal pore area is heterogeneous across leaf surfaces. This has been considered as “patchy stomatal conductance,” and may have substantial implications for photosynthetic efficiency. Aerosols have always been important elements of plant environments, but their effects on stomatal control of plant water relations, and stomatal heterogeneity speci...
Article
Full-text available
Coffee quality is a complex trait involving sensory and bean characteristics as well as biochemical contents. The objective of this study was to assess the major factors influencing the quality of wild Arabica coffee (Coffea arabica L.) in the natural coffee forests of southwest and southeast Ethiopia. Results revealed that both natural (soil, aspe...
Article
Full-text available
The study was conducted in the natural coffee forest ecosystems of southwest and southeast Ethiopia, where the wild populations of Coffea arabica L. naturally grow. Soil is an important environmental factor that performs different important functions in the terrestrial ecosystems, including in the natural coffee forest ecosystems. The objective of...
Article
Documentation in the field of the longitudinal progression of freezing in woody stems during winter has recently become feasible due to development of advanced instrumentation. Similar techniques to detect the radial progression of freezing fronts in the stem have remained challenging and, so far, unresolved. Here we address this problem with a sma...
Article
Adjuvants such as surfactants are commonly incorporated into agrochemical formulations to enhance the biological efficiency of foliar sprays by improving the wetting behavior of the spray and/or the penetration of the active ingredients into the leaf tissues. Penetration accelerating adjuvants are known to increase the cuticular permeability and ma...
Article
Full-text available
Some 40 years ago, air pollution caused widespread forest decline in Central Europe and eastern North America. More recently, high levels of tree mortality worldwide are thought to be driven by rising temperatures and increasing atmospheric drought. A neglected factor, possibly contributing to both phenomena, is the foliar accumulation of hygroscop...
Article
Aerosols are important components of the global plant environment, with beneficial and deleterious impacts. The direct effects of aerosol deposition on plant–water relationships remain poorly characterized but potentially important. Vicia faba was grown in ambient urban air and in the same air with aerosol excluded, in a moderately polluted environ...
Article
The precise understanding of the interactions of adjuvants, agrochemicals and foliar fertilizers is essential to improve the efficacy of spray applications. In this study, we explored the influence of manganese foliar fertilizers (manganese sulfate and manganese nitrate) tank-mixed with an insecticide (chlorantraniliprole) and one organosilicone su...
Article
Full-text available
Previous flux measurements in the perhumid cloud forest of northeastern Taiwan have shown efficient photosynthesis of the endemic tree species Chamaecyparis obtusa var. formosana even under foggy conditions in which leaf surface moisture would be expected. We hypothesized this to be the result of 'xeromorphic' traits of the Chamaecyparis leaves (hy...
Chapter
Atmospheric aerosols are liquid, solid, or mixed suspensions of heterogeneous chemical composition, ranging from a few nanometers to almost 100 μm in diameter. Plants are sources and sinks of these diverse aerosols. Vegetation is influenced by aerosols through the water cycle, radiation balance, and nutrient transport, on global and regional scales...
Article
The atmospheric vapor pressure deficit (vpd) is the driving force for plant transpiration. Plants have different strategies to respond to this ‘atmospheric drought.’ Deposited aerosols on the surface of plant leaves can interact with plant water relations and may influence the vpd response of plants. We studied the transpiration and water use effic...
Chapter
The background for this discussion was the background document in this book entitled: “Surface/atmosphere exchange of atmospheric acids and aerosols, including the effect and model treatment of chemical interactions”.
Article
Full-text available
Ammonia exchanges between the atmosphere and terrestrial ecosystems are composed of several pathways including exchange with the soil, the litter, the plant surfaces (cuticle) and through the stomata. In this study, the fate of nitrogen in the different pools (soil and plant) was analyzed with the aim of determining the sources and sink of atmosphe...
Chapter
Chemical processes occurring on leaf surface and in air inside vegetation canopies play significant and sometimes dominant roles on pollutant dry deposition budgets. Yet, these processes are seldom explicitly treated in dry deposition parameterizations/models. This report briefly summarizes the current knowledge, outstanding issues, and recommendat...
Book
The background for this discussion was the background document in this book entitled: “Surface/atmosphere exchange of atmospheric acids and aerosols, including the effect and model treatment of chemical interactions”
Book
Chemical processes occurring on leaf surface and in air inside vegetation canopies play significant and sometimes dominant roles on pollutant dry deposition budgets. Yet, these processes are seldom explicitly treated in dry deposition parameterizations/models. This report briefly summarizes the current knowledge, outstanding issues, and recommendat...
Article
Since a key requirement of known life-forms is available water (water activity; aw ), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggest...
Article
There is various evidence that the presence of condensed water, e.g. dew, improves plant water relations. Since particularly plants in drier environments are expected to benefit from atmospheric water, it may be assumed that special adaptations promoting exploitation of dew water evolved in these habitats. Surface characteristics affect dewfall and...
Article
The objective of this study was to better understand the role of chaotropic and kosmotropic salts in stomatal uptake, a process that occurs in parallel with cuticular penetration and affects the bioefficacy of glyphosate. In Trial 1, salt solutions of kosmotropic (NH4)2SO4 and chaotropic NaClO3, with or without the organosilicone surfactant, Break-...
Article
Full-text available
"Microscopic leaf wetness" means minute amounts of persistent liquid water on leaf surfaces which are invisible to the naked eye. The water is mainly maintained by transpired water vapor condensing onto the leaf surface and to attached leaf surface particles. With an estimated average thickness of less than 1 μm, microscopic leaf wetness is about t...
Article
Full-text available
The study was carried out to determine the variations among different Coffea arabica germplasm lines in hydraulic resistances under controlled nursery settings at the Jimma Agricultural Research Center in southwest Ethiopia. The experimental treatments included contrasting shade conditions (moderate shading v. full sunlight) and seedlings of 12 ara...
Article
Air pollution causes the amorphous appearance of epicuticular waxes in conifers, usually called wax 'degradation' or 'erosion', which is often correlated with tree damage symptoms, e.g., winter desiccation. Previous investigations concentrated on wax chemistry, with little success. Here, we address the hypothesis that both 'wax degradation' and dec...
Article
Full-text available
Bananas are frequently grown in coffee and cacao agroforestry systems. We asked whether tree shade affects leaf photosynthesis beyond simply the effects of the reduction in light availability. Does the leaf compensate for lower light availability to achieve greater than expected leaf photosynthesis? In this study, the photosynthetic performance at...
Article
Aerosols are an ubiquitous component of the atmospheric environment of plants but their ecophysiological role is largely unknown. Here we address this role by comparing the water relations of plants grown in ventilated greenhouses with ambient air (AA), and filtered air (FA) where particle concentrations had been reduced by more than 99%. Beans and...
Article
Full-text available
The study was carried out with the objective to compare the variations in root growth characteristics of wild Coffea arabica populations in Ethiopia. A total of 24 wild coffee trees were used for in-situ root growth measurements under four natural coffee forests, viz., Harenna, Bonga, Birhane-Kontir and Yayu. Analysis of variance was performed to c...
Article
Full-text available
The study was conducted with the aim of determining the variations in growth and hydraulic resistances and identifying the relationship between these traits in seedlings of Arabica coffee populations. Coffee accessions collected from four wild coffee forests in Ethiopia (Harenna, Bonga, Berhane-Kontir and Yayu) were ex situ evaluated under control...
Article
The recent visualization of stomatal nanoparticle uptake ended a 40-yr-old paradigm. Assuming clean, hydrophobic leaf surfaces, the paradigm considered stomatal liquid water transport to be impossible as a result of water surface tension. However, real leaves are not clean, and deposited aerosols may change hydrophobicity and water surface tension....
Article
Full-text available
The study was conducted with the aim to compare the variability among the wild coffee germplasm accessions in diurnal leaf water potential (LWP, ΨL) under contrasting shading and irrigation environments. Twelve coffee accessions were evaluated under two shading (moderate shading and full sun radiation) and irrigation (well watered and water stresse...
Article
Full-text available
The study was carried out with the objective to investigate the variations among Coffea arabica L. accessions in water conductance under contrasting nursery environments at the Jimma Agricultural Research Center, southwestern Ethiopia. The treatments included two shade (moderate shading and full sunlight) and two irrigation (well watered and water...
Article
Full-text available
The montane rainforests of Ethiopia are the only known centres of origin and genetic diversity for Coffea arabica . However, the remnant coffee forest environments with the spontaneously grown wild coffee populations are under continuous threat of genetic erosion, largely due to anthropogenic activities. The study was conducted with the objective t...
Conference Paper
Full-text available
Sixty smallholders intercropping coffee, banana (Musa spp.) and trees in Central Costa Rica and Northern Nicaragua were described, of which twenty farms were intensively investigated. The aim of this work was to describe and analyse the coffee agroforestry system with focus on banana production. This was based on the assumption that bananas have to...
Article
Aerosols have always been part of the atmosphere, and plant surfaces are a major aerosol sink. Given the nutrient content of aerosols and the natural stability of aerosol concentrations over evolutionary time, plants may have developed adaptations to aerosol input. Although little is known about such adaptations, leaf surface micro-roughness appear...
Article
Theoretical explanations of dew formation usually consider a pure, plain surface and do not include any contributions of hygroscopic material present on this surface. A significant amount of hygroscopic material, however, is present on most real leaves, due to accumulated deposited aerosols, salt exudations, leached ions, or agricultural sprays. Si...
Chapter
Full-text available
The income-generating activities in the Middle Draa valley are strongly based on water use and land resources. Nevertheless, labor migration and tourism increasingly help to diversify the sources of income for farm and pastoral households. The most important component of water demand in the Draa basin is crop production in the oases of the Middle D...
Article
Full-text available
The montane rainforests of Ethiopia are the known centres of origin and genetic diversity for Coffea arabica. However, the remnant rainforests with the spontaneously grown wild coffee populations are under continuous threat, largely due to population pressure, indiscriminate deforestation and extensive disturbance of the natural forest habitats, an...
Article
Full-text available
Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological para...
Article
Ecosystems and the atmosphere: This review describes the state of understanding the processes involved in the exchange of trace gases and aerosols between the earth's surface and the atmosphere. The gases covered include NO, NO2, HONO, HNO3, NH3, SO2, DMS, Biogenic VOC, O3, CH4, N2O and particles in the size range 1 nm–10 μm including organic and i...
Conference Paper
Nutrient input by atmospheric particles is important or even essential for forest ecosystems. Many particles will first deposit to leaf surfaces. Competition is avoided by direct foliar uptake, compared to uptake via the soil. While there is meanwhile clear evidence for foliar uptake to happen via the stomata under natural conditions, this requires...
Article
Full-text available
A major international experiment on ammonia (NH<sub>3</sub>) biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH<sub>3</sub> exchange including: a) quantification of nearby emissions and advection...
Article
Full-text available
Ammonia exchange fluxes between grassland and the atmosphere were modelled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the GRAMINAE intensive measurement campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew chemistry in grassland were measured together with am...
Conference Paper
Full-text available
A study to establish a relationship between cup quality of coffee and soil properties was conducted in the coffee forest ecosystem of south western Ethiopia, the home of wild Arabica coffee. Cup quality of coffee depends on different factors such as the type of coffee, soil conditions, climatic conditions, processing methods etc. The present paper...
Conference Paper
Full-text available
A study on four commonly found indigenous coffee shade tree species (Acacia abyssinica, Albizia gummifera, Albizia schimperiana, and Cordia africana) was conducted in the Afromontane rainforests of Ethiopia to assess their effects on the physical and sensory quality of wild Arabica coffee. Results showed that sensorial differences in wild Arabica c...
Article
Full-text available
A study to establish a relationship between cup quality of coffee and soil properties was conducted in the coffee forest ecosystem of south western Ethiopia, the home of wild Arabica coffee. Cup quality of coffee depends on different factors such as the type of coffee, soil conditions, climatic conditions, processing methods etc. The present paper...
Article
Full-text available
Ammonia exchange fluxes between grassland and the atmosphere were modeled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the GRAMINAE intensive measurement campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew chemistry in grassland were measured together with amm...
Article
A standardized method of moss exposition for assessing variations in nitrogen deposition was tested in the western part of Germany. Six pleurocarpous moss species were transplanted to two sites differing in their deposition rates but being comparable as to their climatic conditions. The mosses were exposed in standardized containers over a period o...
Article
The suitability of the two pleurocarpous mosses Pleurozium schreberi and Scleropodium purum for assessing spatial variation in nitrogen deposition was investigated. Sampling was carried out at eight sites in the western part of Germany with bulk deposition rates ranging between 6.5 and 18.5 kg N ha(-1) yr(-1). In addition to the effect of depositio...
Chapter
Full-text available
This book contains seventeen chapters discussing the economic and biological aspects of soil use and research in agroforestry, with an emphasis on nutrient-poor forest and savanna soils. Topics covered include the economics of soil fertility management, cycling of water, nutrients and organic matter, soil structure, soil water, root systems, soil b...
Article
In this study the influence of air humidity, light, concentration and position on the leaf blade on the uptake of the anionic fluorescent dye uranine (sodium fluoresceinate) was investigated, using isolated epidermal strips (ES) of Allium porrum and of the ornamental plant Sedum telephium. The dye was applied in aqueous solution as single droplets...
Article
Electrical conductance (λ) was measured continuously and in vivo on leaf surfaces of Vicia faba and Aegopodium podagraria. λ increased with rise and decreased with fall in humidity, exhibiting a hysteresis during an applied humidity cycle [90–20–-90% relative humidity (r.h.)]. After treatment with NaNO3 aerosols, a sudden increase in λ was observed...
Article
Full-text available
The land use / land cover of an area is a key parameter within the hydrological cycle. In the framework of IMPETUS (Integrated management project for a sustainable use of fresh water) the Vegetation Group are investigating the complex interactions between the hydrological cycle and vegetation in two river catchments, situated north and south of the...
Article
Stomatal conductance, which controls both the exchange of water vapour and CO2, is thought to be strictly determined by stomatal aperture. However, water transport processes might be modified by deposition of hygroscopic salts on the leaf surface. For this reason, simultaneous measurements of gas exchange and stomatal aperture were performed on Sam...
Article
A large fraction of deposited aerosol particles on leafsurfaces represents hygroscopic material in a high humidity environment, likely to become deliquescent within the water vapour transpired by the leaf. Microscopic observations on leaf surfaces of beech, kohlrabi and elder leaves grown in a particle-free environment and/or treated with defined p...
Article
Evidence for stomatal uptake of solutes by leaves without the application of surfactants or pressure has recently been provided (Eichert et al., 1998). In the present study, experimental conditions were refined in that the water potential was held at <0 on the physiologically inner side of the epidermal strips (ES) by use of a ceramic plate or the...
Article
The possibility of stomatal uptake of ions has recently been demonstrated, contrary to the widespread opinion rejecting this possibility for physical reasons. We tested the importance of stomatal uptake of foliar applied nutrients into leaves under field conditions, at a research site near Manaus, central Amazonia, Brazil , on orange (Citrus sinens...
Article
: Experiments were conducted with leek (Allium porrum L.) leaves to investigate whether aqueous solutions are able to penetrate stomata. Epidermal strips were used for the determination of transport rates. Stomata were opened by fusicoccin or closed by darkness or abscisic acid. A droplet containing the anionic fluorescent dye, uranine, was placed...
Article
Ammonia fluxes over vegetated land are bi-directional, with differences between emission and deposition occurring in relation to environmental conditions (temperature and wetness), plant community (e.g. arable land, unfertilized ecosystems), as well as other factors such as plant phenology. In the present paper, measurements of net NH3 fluxes over...
Article
Atmospheric ammonia (NH3) concentrations were measured using a continuous-flow annular denuder over a period of 2 yr at a rural site near Edinburgh, Scotland. Meteorological parameters as well as sulphur dioxide (SO2) concentrations were also recorded. The overall arithmetic mean NH3 concentration was 1.4 μg m-3. Although an annual cycle with large...
Article
Abiogenic N2O production was observed on aerosols collected by a high volume sampler. Dependent on relative humidity, 0.03–0.085 nmol N2O per mg aerosol (dry weight) was formed during 48 h of incubation. From pure salts containing ammonium and nitrate, N2O was emitted at lower rates compared to airborne aerosols. This may be due to differences in t...
Article
Four year old spruce (Picea abies (L.) Karst.) seedlings were planted in sand pots and supplied with nutrient solution. Three groups were formed, differing only in manganese nutrition (0.5 ppm, 2.5 ppm, 12.5 ppm, respectively). After three months, five individuals of each group were transferred to a dew chamber. For the next seven weeks the trees w...
Article
Micrometeorological measurements of the exchange of atmospheric ammonia over arable land are reported. Measurements were made over bare soil and wheat canopies at early canopy closure, approaching anthesis and during early senescence. Bare soil showed a slow rate of deposition with a canopy resistance (Rc) of around 300 s m−1, while fluxes over you...
Article
The deposition of fine particles, consisting largely of ammonium and sulphate, as well as the deposition of SO2 and NH3, is often dependent on processes happening in the last mm of the atmosphere above the plant surface. Surface wetness plays an important role for trace gas deposition, and at the same time creates a link between particle and trace...
Article
Forest decline has been observed for about 20 years, especially in Central Europe and eastern North America. Whereas the direct effects of acid rain, acid fog and several trace gases on aerial parts of trees have been investigated, deposited atmospheric particles on leaf surfaces have been regarded as inert so far. By conductance measurements on th...
Article
Micrometeorological measurements of atmospheric ammonia (NH3) exchange with semi-natural and agricultural plant communities were made using sensitive new instrumentation capable of determining NH3 fluxes at g m–3. The results are used to test hypotheses concerning the canopy cycling of reduced nitrogen (NHx) and the existence of potential feedbacks...
Article
Monodisperse particles (particle diameter ≈0.5 μm) were produced by a particle generator and tagged witha fluorescent dye. The particles were injected into asmall wind tunnel, into which single needles or small branches of Picea abies, Pinus sylvestris, and Abies alba had been introduced. The needles were examined after treatment, using fluorescenc...
Article
Wetness measurements were conducted directly on the surface of coniferous needles by means of specially designed wetness sensors in different heights of a 40-year-old spruce canopy. During the observation time from May to October, 1992, the wetting by rain amounted to about 28% of the time, not differing significantly with the height of the tree. I...
Article
This note describes the construction and application possibilities of newly developed surface wetness sensors. At the present state of sensor development the absolute values are not reproducible. However, even the relative conductance measurements allow the detection of non-visible water films on samples in the laboratory as well as in the open fie...
Article
Measurements of the electrical conductivity along the surface of leaves or conifer needles show that the wetting of such surfaces coated with wax already starts below a relative humidity of 100%. To explain the observations, the deposition of water soluble atmospheric aerosol particles on these surfaces is taken into account. It is shown that the c...
Article
Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. T...

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